Idk if this is true or not, but I read somewhere here in the comments from the past that Cosset isn’t even a human... but a demon.
Cosette isnt even alive and was a stillborn and then a demon inhabited the body so technically the real cosette is the real daughter of the grand duke. The demon inhabited the body to take over the world i think
Its true that the prev wife of the king had a child, but it was a son, not a daughter.. I don't really know what happened, but i think she made a contract? With a devil, and the devil turns into a daughter.. that's why she can steal the mc's power, i think...
Some spoilers please they're greatly appreciated thank you